Twenty-seven were dead and 64 wounded in the Sunday night attack near a hospital and a school near Aleppo's municipal stadium, state TV and the official Syrian Arab News Agency said.
The opposition Local Coordination Committees of Syria also reported 27 killed in Aleppo but said the people were killed by regime artillery shelling.
Aleppo is divided into rebel- and regime-controlled districts, with opposing forces fighting for full city control for more than six weeks.
The Syrian media blamed the explosion on "terrorists," the term the regime typically uses for opposition fighters seeking to oust President Bashar Assad.
While the official media referred to a "terrorist bombing," Aleppo provincial Gov. Mohammed Wahid Akkad was quoted on semi-official pro-government Addounia TV as saying two car bombs may have been involved in the attack.
The Halab al-Shahbaa rebel brigade claimed responsibility along with two other units, claiming the military had turned two hospitals into barracks.
State TV said one of the dead was an 18-year-old nurse. It showed video of a man exclaiming, "I know her -- she is a nurse in the hospital!"
"This is the freedom you want?" the man said, in translation provided by the Los Angeles Times. "These were hospitals treating people!"
Fighting also raged around the capital, Damascus, as Syrian troops were reported to have closed in on a neighborhood near the city boundary that was once the Yarmouk refugee camp populated by Palestinians.
Regime forces pounded presumed opposition strongholds with tanks, artillery and attack helicopters, The New York Times reported.
The coordination committees said 40 people were killed in Damascus and its suburbs from shelling and gunfire.The committees also reported regime forces launched raids and indiscriminate arrests in the Yarmouk neighborhood.
All told 160 were killed in Syria Sunday, including nine killed in a massacre in the western city of Rastan, 12 miles north of Homs, the committees said.
Attack reports and death tolls cannot be confirmed because of Syrian regime restrictions on independent journalists.
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